title: Evaluation of passive samplers with neutral or ion-exchange polymer coatings to determine freely dissolved concentrations of the basic surfactant lauryl diethanolamine: Measurements of acid dissociation constant and organic carbon-water sorption coefficient.
abstract: A passive sampler tool (solid-phase microextraction, SPME) was optimized to measure freely dissolved concentrations (Cw,free) of lauryl diethanolamine (C12-DEA). C12-DEA can be protonated and act as a cationic surfactant. From the pH-dependent sorption to neutral SPME coatings (polyacrylate and PDMS), a pKa of 8.7 was calculated, which differs more than two units from the value of 6.4 reported elsewhere. Polyacrylate coated SPME could not adequately sample largely protonated C12-DEA in humic acid solutions of pH 6. A new hydrophobic SPME coating with cation-exchange properties (C18/SCX) sorbed C12-DEA 100 fold stronger than polyacrylate, because it specifically sorbs protonated C12-DEA species. The C18/SCX-SPME fiber showed linear calibration isotherms in a concentration range of <1 nM-1 μM (well below the CMC). Using the C18/SCX-SPME fibers, linear sorption isotherms to Aldrich humic acid at pH 6 (ionic strength 0.015 M) were measured over a broad concentration range with a sorption coefficient of 10(5.3).
authors.affiliation: College of Environmental Science and Engineering, Ministry of Education Key Laboratory of Pollution Processes and Environmental Criteria, Tianjin Key Laboratory of Environmental Remediation and Pollution Control, Nankai University, Wei Jin Road 94, Tianjin 300071, China.
authors.forename: Fang
authors.initials: F
authors.lastname: Wang
authors.forename: Yi
authors.initials: Y
authors.lastname: Chen
authors.forename: Joop L M
authors.initials: JL
authors.lastname: Hermens
authors.forename: Steven T J
authors.initials: ST
authors.lastname: Droge
mesh_terms: D000327:Adsorption; D002412:Cations / Q000737:chemistry; D002853:Chromatography, Liquid; D004785:Environmental Pollutants / Q000032:analysis; D004983:Ethanolamines / Q000032:analysis*; D006812:Humic Substances / Q000032:analysis; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007850:Lauric Acids / Q000032:analysis*; D052617:Solid Phase Microextraction / Q000379:methods*; D013501:Surface-Active Agents / Q000032:analysis*; D053719:Tandem Mass Spectrometry
chemical_list: D002412:Cations; D004785:Environmental Pollutants; D004983:Ethanolamines; D006812:Humic Substances; D007850:Lauric Acids; D013501:Surface-Active Agents
keywords: Cation-exchange; Cationic surfactant; Humic acid; SPME-fibers; Sorption; pK(a)